Three-dimensional integrated circuits (3DICs) include top chips stacked on a passive interposer. The top chips are electrically connected to the passive interposer through micro solder bumps. In some instances, the passive interposer includes through substrate vias (TSVs) and metal routing layers configured to provide electrical connection from a surface of the passive interposer connected to the top chips and an opposite surface of the passive interposer. In some instances, the opposite surface of the passive interposer is electrically connected to a substrate by solder bumps. In some instances, TSVs are configured to provide electrical connection between a surface of the substrate in contact with the passive interposer and an opposite surface of the substrate.
One way to test the quality of the connection between the top chips and the passive interposer as well as between the passive interposer and the substrate is to form Kelvin structures on the 3DIC. A Kelvin structure includes a group of four testing sites, electrically connected to the micro solder bumps and/or the solder bumps between the passive interposer and the substrate. The Kelvin structure is arranged to test the resistance of solder bumps. By passing a voltage through two of the testing sites of the Kelvin structure and measuring a resulting current in the other two testing sites of the Kelvin structure, a resistance value of the micro solder bumps and/or the solder bumps between the passive interposer and the substrate can be determined. The resistance value provides information regarding whether the micro solder bumps and/or solder bumps provide sufficient electrical connection between the various components of the 3DIC.